Some embodiments are directed to high-electromagnetic-impedance surface (or HIS, for “High Impedance Surface”) devices.
In some fields, like that of satellite positioning signal receivers for example, surface devices with high electromagnetic impedance are used. The latter can, for example, be used to reduce the electromagnetic couplings between elements in multistandard adaptive networks.
It is recalled that a surface device with high electromagnetic impedance generally comprises a ground plane, at least one dielectric cavity (generally in the form of a substrate), and a printed circuit board (PCB), which is single-layer or multilayer, and comprising a multitude of conductive elements defining patterns arranged periodically and of small size and periodicity compared to the wavelength used.
When there is a desire for the surface device with high electromagnetic impedance to exhibit at least two resonant frequencies, it is possible, for example, to arrange it as described in the patent document U.S. Pat. No. 6,670,932. More specifically, this surface device with high electromagnetic impedance is of mushroom type, that is to say that it comprises a conductive ground plane defining a non-compartmentalized cavity but comprising a matrix of identical conductive pillars, filled with a dielectric material and covered by a printed circuit board bearing metallic patterns, in order to form electromagnetic resonators exhibiting different resonant wavelengths. The size and the periodicity of the elements (or “patches”) defining the patterns is smaller than the resonant wavelengths of the electromagnetic resonators.
Each pattern is intended to capture, at the input of the cavity, an incident electromagnetic wave which is propagated in the ground plane, then to generate, under the pattern, an electric current loop at a determined resonant frequency so as to reflect any incident electromagnetic wave having a frequency in a narrow band centered around this resonant frequency.
The device described offers an interleaving of a first “matrix” of electromagnetic resonators that are identical and that have a first resonant frequency, with a second “matrix” of electromagnetic resonators that are identical and that have a second resonant frequency. This interleaving is obtained by the patterns which are borne by the printed circuit board of fractal or multilayer type, each pattern being centered either on a pillar or between four adjacent pillars.